Semen analysis also known as the “sperm count” or “semen test” remains the standard initial laboratory test in the evaluation of male fertility or infertility. It has been performed for more than half a century with refinements along the way. However, for many men (and couples) it remains limited in its clinical usefulness. Other than at the extremes (ie severe low sperm count or absent sperm), there remains an overlap in the distribution of standard parameters of sperm(count, motility and morphology) for fertile and infertile men. In other words, some men conceive despite low numbers and other men may have difficulties despite higher numbers.
Seminal fluid is made up of a mixture of ingredients originating from different genital organs including the testis, epdididymis, prostate and seminal vesicles and cowpers glands. The fifth edition of the WHO laboratory for the examination and processing human semen recommends Sexual abstinence of 2-7 days before submission of a sample for analysis. Interestingly, there has been some investigation as to whether subfertile men, should submit samples after only 1 day of sexual abstinence.
How is Semen Analysis Preformed?
The WHO manual uses a sperm concentration of 15M/ml as the most recent standard discriminant for a normal semen analysis; this reflects the count of the fifth percentile or count in the lowest 5% of a fertile population. However, some studies show a decrease in time to conception with increasing sperm concentration up to 40M/ml, with no apparent additional benefit with a higher sperm density. Similarly, although sperm strict morphology (shape) of greater than or equal to 4% correlates with the previously mentioned fifth percentile, a higher strict morphology has similarly been associated with faster time to conception.
What are the constraints of the semen analysis? The semen analysis represents an attempt to predict fecundity by what one can see on a microscope slide. Therefore the limitations of semen analysis are inherent to what the test is not able to look at.
There is more to sperm fertilizing an egg than their number, how they move and what they look like.
There are a number of steps to fertilization that simply don’t occur until sperm comes up against the egg and its environment. Once the sperm reaches the fallopian tube, several things need to happen:
- The sperm has to undergo a processes called “capacitation”. Capacitation involves molecular changes such as sperm protein tyrsosine phosphorylation which is required for sperm to be able to fertilize an Egg.
- The sperm must penetrate the layers surrounding the egg: the cumulus and the zona pellucida.
- When it meets the zona pellucida , it must undergo “hyperactivation” relating to a fundamental change in the movements of the sperm tail as well as the “acrosome reaction” which involves release of enzymes located at the front portion of the head of the sperm known as the acrosome.
- At the same time, and then it has to fuse with and then fertilize the egg , a process which requires certain sperm surface proteins to be present.
There is a need for further development of sperm tests.
So, although the semen analysis(SA) may be very accurate in its assessment of what it can look at, and although there is some predictive ability of the SA, It’s clear that the semen analysis has some limitations. Looking to the future, there is a need for the development of functional sperm tests that have validated clinical utility in terms of their being able to discover impaired fertility. It would be better still if the identification of functional problems would also yield solutions to fix those problems.